Large spherical valves, especially those designed for pumped storage operation, require special design considerations due to their size. A problem with large spherical valves is their inability to completely seal off water flow. For this purpose, the piston seal ring must conform not only to the axial displacement of the stationary rotor seat ring but must also adapt to rapid change of this displacement along the rotor seat ring due to the nonuniform stiffness of the rotor seal support. If the downstream seal is not able to seat, auto-oscillation, a serious and damaging dynamic phenomenon, can occur in the penstock system valve.
In known spherical valves, to accommodate the nonuniform seat ring deflections different approaches have been used. One approach uses flexible metallic seals. Another approach uses rubber seals. Still another approach utilized rubber inserts added to the stationary metal seat ring. However, none of these approaches have proved completely satisfactory.
Accordingly, the present invention involves only metal sealing contacts. The stationary seat ring thickness contour is machined so that a substantially flat sealing surface is presented after the rotor is closed under maximum static head. This insures substantially 100% contact and near uniform contact stress between the piston seal and the seat ring all around the circumference of their contact.
The general object of the present invention is to provide a metallic stationary or fixed rotor seat ring seal which insures substantially uniform engagement by the movable piston ring seal despite large differential deflections of the fixed rotor seat ring seal.
A more specific object of the present invention is to provide a rotor seal ring seal whose seating surface is formed so as to be in a single plane when the rotor is loaded.